Existing treatments for pulmonary fibrosis have not significantly improved survival; there is a critical need for new approaches. A combination of environmental and genetic factors creates an alveolar epithelium that is susceptible to injury from either endogenous or exogenous factors. Deregulated repair of damaged tissue leads to the hyperplastic and proliferating alveolar type II cells (AECII) - the so called re-programmed AECII, which are main pathological features in the lungs of patients with fibrosis. Re-programmed AECIIs play a key role in the pathogenesis of pulmonary fibrosis, producing TGF-? and pro-inflammatory mediators leading to activation of lung fibroblasts and recruitment of macrophages that further deregulate repair. Our long-term goal is to dissect transcriptional regulation of pulmonary fibrosis. We recently identified a novel pro-fibrotic regulator, Foxm1, a member of the family of Forkhead Box (Fox) transcription factors. Our preliminary data demonstrated that Foxm1 is induced in AECII within fibrotic lesions, but not in normal alveolar region of human and mouse lungs, indicating that Foxm1 can be a marker of re-programmed AECIIs. Transgenic expression of activated Foxm1 transcript in mouse AECII exacerbated radiation-induced pneumonitis and caused severe pulmonary fibrosis. Conditional deletion of Foxm1 from AECII attenuated radiation-induced lung fibrosis. While these data demonstrate that AECII promote pulmonary fibrosis through Foxm1-mediated events, the downstream signaling pathways regulated by Foxm1 in AECII remain to be identified (objective). The goal of this proposal is to test central hypothesis that AECII promote pulmonary fibrosis through Foxm1-mediated activation of fibroblasts and recruitment of myeloid inflammatory cells into fibrotic lesions. By combining genetic and molecular approaches in radiation- and bleomycin-induced mouse models of lung fibrosis, the proposed studies will identify molecular mechanisms regulated by Foxm1 in AECII, and determine Foxm1 contribution in re-programming of AECII cells to promote lung fibrosis. In Aim 1, we will use single cell RNA-Seq analysis and transgenic mice with AECII-specific deletion of Foxm1 to identify transcriptional signatures of Foxm1 in re- programmed AECII. Since our preliminary data show increased expression of pro-fibrotic and inflammatory mediators in Foxm1-overexpressing AECII, we will examine whether Foxm1 activates transcription of Osteopontin and TGF?1 genes in AECII, and stimulates activation of latent TGF?1 protein, causing activation of lung fibroblasts. In Aim 2, we will examine whether Foxm1 activates CCL2 and CXCL5 genes in AECII, leading to recruitment of myeloid inflammatory cells into fibrotic lungs. We will also use novel small molecule Foxm1 inhibitor recently discovered in our laboratory to inhibit Foxm1-induced reprogramming of AECII, lung inflammation and fibrotic remodeling in murine models of pulmonary fibrosis. Completion of our studies will (1) identify novel molecular mechanisms by which Foxm1 induces pulmonary fibrosis, and (2) test therapeutic strategy of targeting Foxm1 to decrease lung fibrosis.